STAGES IN DEVELOPMENT OF MOLLUSKS, PALEOBIOGEOGRAPHY OF BOREAL SEAS IN THE EARLY-MIDDLE JURASSIC AND ZONAL SCALES OF SIBERIA
S.V. Meledina, B.N. Shurygin, and O.S. Dzyuba
Institute of Petroleum Geology, Siberian Branch of the RAS,
3 prosp. Akad. Koptyuga, Novosibisrk, 630090, Russia
Keywords: Early Jurassic, Middle Jurassic, paleobiogeography, stratigraphy, ammonites, belemnites, bivalves, northern Asia
Pages: 237-254
Abstract
We compared stages of the taxonomic restructurings that occurred in communities of ammonites, belemnites, and bivalves in Siberian sea basins in the second half of the Early Jurassic and at the beginning of the Middle Jurassic. In general, the main stages are similar in different groups of mollusks, but the restructuring borders often do not coincide. Degree of endemism and portion of immigrants in communities of different groups differ as well. Abiotic factors that have an effect on the evolution and migration are addressed here. On the basis of areal differentiation of mollusk assemblages, three paleobiogeographic areas have been recognized since the Late Pliensbachian: circumpolar Arctic, western Boreal-Atlantic and eastern Boreal-Pacific Realms. These realms are united into the Panboreal Superrealm. Ammonite, belemnite, and bivalve zonal scales devised for the Siberian Jurassic reflect the specific evolution of each of these groups in seas of the Arctic Realm as well as specific variations in its communication with adjacent realms.
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